2. Field of the Invention
This invention relates to an apparatus and method for processing of fish, e.g., for the outdoor drying of fish, particularly squid, or for the smoking of fish, or for the individual quick freezing of fish.
2. Description of the Prior Art
Outdoor drying of fish is well known as being the most economical means of drying fish, particularly in remote fishing villages. Generally, this consists merely of spreading the fish to be dried on an outdoor platform and to wait until the ambient atmospheric conditions dry the fish. Since ambient atmosphere is used, drying is subject to the vagaries of the ambient atmosphere. Particularly harmful are periods of precipitation. Outdoor drying of squid is particularly troublesome due to the non-uniform irregular shapes of squid.
Fish nowadays may be cured by drying, smoking, salting, or pickling. In the drying process, the step of drying fish by blowing warm dry air on them as largely replaced sun drying in some areas.
Other fish, e.g., herring, salmon, smelt and mackerel are smoked. The cleaned fish are salted, washed and drained and then hung on frames to dry. Then they are hung in the smokehouse for curing.
Freezing keeps fish longer and generally in better condition than other curing techniques. Quick freezing at extremely low temperatures ensures fresh flavour and texture. The fish are placed on a conveyor and are passed through a freezing tunnel, where they are sprayed with liquid nitrogen to freeze them, the so-called Individual Quick Freezing (I.Q.F.).
The processing of fish has been the subject of patents for many years. Canadian Pat. No. 53,009 "Method of and Apparatus for Smoking Fish," issued July 22, 1896 to Carl Waldemann, teaches a process of smoking fish consisting of cutting the fish in longitudinal sections, placing a piece of membranous or similar appropriate material upon the inner split surface, and laying the fish upon a frame over the smoke. The frame, which holds the fish while being smoked, consists of a number of triangular transverse frame pieces having base ledge projections and wire screen surfaces fitted thereon and also inclined in opposite directions.
Canadian Pat. No. 205,314 entitled "Process of Kippering Fish" issued Nov. 2, 1920 to Carl G. Villen, describes a fish preserving process which includes the first step of subjecting the fish to the action of smoke under pressure, and finally to the step of subjecting the smoked fish to a temperature to cook the fish.
Canadian Pat. No. 294,184 entitled "Process of Smoking Fish Fillets" issued Oct. 22, 1929 to James R. Turner, provides a process for smoking fish fillets by placing the fresh fillets on a screen and "setting" them therein while the screen is in a substantially horizontal position, and then tilting the screen to a steeply inclined position and passing smoke upwardly past both sides of the screen.
Canadian Pat. No. 236,588 entitled "Refrigeration System" issued Dec. 25, 1923 to Harden F. Taylor, provides a process for freezing fish by suspending them in a vertical position, causing a refrigeration liquid of 0.degree. C. or colder to shower or spray over the fish, and causing the suspended fish to travel through the shower.
Canadian Pat No. 998,973 entitled "Superchilling of Fish" issued Oct. 26, 1976 to Liquid Carbon Canada Ltd., relates to a method of processing and packing fresh fish and fresh fish fillet. It provides an improvement in what is known as "superchilling." This involves cooling the fish to 23.degree.-30.degree. F., a partial freezing or glazing process which affects only the outer layers of fish or fillet. It reduces weepage and shrinkage and curtails bacterial action at that temperature by sealing the surfaces. Superchilling can be achieved by several means: brine tanks or baths, cold rooms, mechanical blast freezers, or other means generally classified as mechanical. However, this application decribes the quickest and most effective way, namely the use of an expendable refrigerant, for example, liquid nitrogen, liquid argon, liquid air, or liquid carbon dioxide. All absorb heat from the fish by going through a change of state and becoming gas and are subsequently either exhausted or recirculated and exhausted. Usually the refrigerant liquid first flashes to liquid and gas with the liquid subsequently evaporating; however, at atmospheric pressure liquid carbon dioxide forms gas and solid with the solid phase, in the form of dry ice snow, ultimately subliming to gas. One known apparatus for carrying out this method involves the use of a hood and the refrigerant is dispensed on top of the contents of an insulating box essentially box-by-box or sequentially. An alternative apparatus involves using a tunnel or spiral refrigerator to cool a number of uninsulated boxes at a time employing both gas and solid/liquid phases. A third apparatus has been envisaged in which dry ice nuggets, pellets, or slabs, are applied to the fish.
The patentee's development uses the broad principles of superchilling. An important feature is the speed with which the fish is chilled to the 28.degree.-30.degree. F. range. With expandable refrigerant, particularly dry ice snow, this is about 1-2 hours when the fish is initially at 55.degree. F. and approximately 0.11 lb. of dry ice snow per lb. of fish is used. This is about one-sixth of the amount necessary to freeze the fish. In a typical embodiment of the patentee's invention, the proper amount of dry ice is produced by flashing with approximately 0.25 lb. of liquid carbon dioxide per lb. of fish. The dry ice snow sublimes and disappears, leaving its refrigeration in the fish. Thus, the patentee provided a process of packing and preserving fish, comprising superchilling a layer of fish or fillet by snowing with an amount of a normally gaseous expendable cryogenic refrigerant, and enclosing the resulting product with an insulating container.